I. Field of the Invention
A novel storage stable, ice-proof adhesive for labeling bottles is provided which comprises an alkaline mixture of starch, a zinc salt of a carboxylated styrene-acrylate resin, peptizer and water.
II. Brief Description of the Prior Art
Ice-proof or cold water resistant labeling adhesives have been used for many years for conditions where extreme humidity resistance and label removal are required as, for example, in labeling beer and soda bottles, and pharmaceutical containers. Heretofore, most of these adhesives were based on casein in combination with metallic salts; however, the problems associated with caseins, e.g. cost, availability, variations in quality, etc., instigated searches for casein substitutes, especially those based on low cost, readily available starches.
Recently adhesives based on starch and ammonium salts of styrene-maleic anhydride resins have been proposed as represented by those described in U.S. Pat. Nos. 3,939,108 and 3,857,803. Similar adhesive systems have also been prepared based on carboxylated styrene-acrylate resins. Ordinarily, such adhesives have provided a satisfactory degree of water-resistance, and in some cases label removability. However, they have suffered drawbacks in their tendency to be unstable either on aging or in reproducibility and in their less than optimum machining or rheological properties. Thus, with respect to stability characteristics, in some instances it has been difficult to reproduce batches substantially uniform in viscosity, stability and machinability from a given formula, without making expensive and time-consuming adjustments upon each batch. Moreover, even when batches appeared satisfactory initially, after aging for 2 or 3 month periods, samples were found to change in viscosity or consistency, sometimes even pasting-up or gelling in the storage container. As regards rheology, it must be understood that the high speed labeling machines employed in industry require adhesives which are non-stringing, have a long working life and are fast-setting.
There is thus a need in the art for an ice-proof adhesive for labels which possesses good storage stability and rheology without sacrifice in the properties of cold water resistance and label removability.